Cationic Linear Scorpion Peptide Mucroporin Displays Antimicrobial Activity against Neisseria Subflava ^†

The emergence of antibiotic resistance makes the development of a new generation of powerful antimicrobials able to kill super bugs more essential than ever. Linear scorpion venom peptides are a small group of venom peptides that display antimicrobial, anticancer, and anti-inflammatory activities, although, in many cases, they exhibit strong hemolytic activity hindering their further development. Here, we present an improved synthesis of Mucroporin, a linear scorpion peptide of 17 amino acids, isolated from the Chinese Scorpion Lychas Mucronatus. The synthesis was conducted on a Microwave Peptide Synthesizer (Biotage Initiator+) by using an ultra-fast method at elevated temperature, 90 °C, avoiding some common steps in the conventional methods and reducing the total synthesis time by 40% and the total waste by 50% without affecting the purity of the crude peptide, which was calculated to 90%, making the final purification easier than ever. The synthesis was performed by using N-butyl-2-pyrrolidone (NBP), a green alternative to DMF solvent, which is under restriction for use in therapeutic peptides as of December 2023 in EU. Mucroporin was tested for its antimicrobial activity against gram-positive and gram-negative bacterial strains (Escherichia coli, Staphylococcus epidermidis, Neisseria subflava and Streptococcus pneumoniae Strain) by the serial dilution method in liquid cultures of bacteria with a cell density of ~2 × 10⁵ CFU/mL in different concentrations and incubated for 24 h, and then the optical density was measured at 600 nm. Ampicillin was used as a positive control at a concentration of 100 μg/mL. The peptide completely inhibited the growth of Staphylococcus epidermidis and Streptococcus pneumoniae, as expected from earlier studies. Of particular interest is the inhibitory activity of Neisseria subflava at a final concentration of 120 μg/mL. This is the first time that mucroporin has ever been reported to be effective against gram-negative strains; therefore, its activity against Neisseria subflava is of particular interest.